|Coordinate||43,408,802 bp (GRCm38)|
|Base Change||A ⇒ T (forward strand)|
|Gene Name||sialic acid binding Ig-like lectin G|
|Chromosomal Location||43,408,204-43,418,358 bp (+)|
FUNCTION: [Summary is not available for the mouse gene. This summary is for the human ortholog.] SIGLECs are members of the immunoglobulin superfamily that are expressed on the cell surface. Most SIGLECs have 1 or more cytoplasmic immune receptor tyrosine-based inhibitory motifs, or ITIMs. SIGLECs are typically expressed on cells of the innate immune system, with the exception of the B-cell expressed SIGLEC6 (MIM 604405).[supplied by OMIM, Jul 2002]
PHENOTYPE: Mice homozygous for a null allele exhibit increased B-1 cell numbers, increased IgM levels and IgM-producing plasma cells, and produce more IgM autoantibodies. [provided by MGI curators]
|Amino Acid Change||Isoleucine changed to Phenylalanine|
|Institutional Source||Beutler Lab|
|Gene Model||predicted gene model for protein(s): [ENSMUSP00000005592]|
AA Change: I38F
|Predicted Effect||probably damaging
PolyPhen 2 Score 0.987 (Sensitivity: 0.73; Specificity: 0.96)
|Meta Mutation Damage Score||0.2470|
|Is this an essential gene?||Probably nonessential (E-score: 0.072)|
|Candidate Explorer Status||CE: potential candidate; human score: 3.5; ML prob: 0.322|
Linkage Analysis Data
|Alleles Listed at MGI|
|Mode of Inheritance||Unknown|
|Last Updated||2019-09-04 9:38 PM by Diantha La Vine|
|Record Created||2018-01-29 10:16 PM|
The Shenandoah phenotype was identified among N-ethyl-N-nitrosourea (ENU)-mutagenized G3 mice of the pedigree R5713, some of which showed increased frequencies of B1 cells in the peripheral blood (Figure 1).
|Nature of Mutation|
Whole exome HiSeq sequencing of the G1 grandsire identified 51 mutations. The increased B1 cell frequency phenotype was linked by continuous variable mapping to a mutation in Siglecg: an A to T transversion at base pair 43,408,802 (v38) on chromosome 7, or base pair 610 in the GenBank genomic region NC_000073. Linkage was found with an additive model of inheritance, wherein three variant homozygotes and 25 heterozygous mice departed phenotypically from 23 homozygous reference mice with a P value of 2.433 x 10-13 (Figure 2).
The mutation corresponds to residue 257 in the mRNA sequence NM_172900 within exon 3 of 12 total exons.
The mutated nucleotide is indicated in red. The mutation results in an isoleucine to phenylalanine substitution at position 38 (I38F) in the Siglec-G protein, and is strongly predicted by PolyPhen-2 to be damaging (score = 0.987).
Siglec-G (Siglec-10 in humans) is a member of the CD33-related Siglec (sialic acid–binding immunoglobulin‐like lectin) family of adhesion molecules. Siglecs specifically recognize sialic acids attached to the terminal regions of cell-surface glycoconjugates; Siglec-G preferentially binds α2,3-linked or α2,6-linked sialic acid (α2,3Sia or α2,6Sia). Sialylated IgM is a known target of Siglec-G (1).
Siglec-C is a type 1 transmembrane protein with a signal peptide, a sialic-binding V-set Ig-like domain, three C2-set Ig-like domains, a transmembrane domain, and a cytoplasmic tail with two putative immune receptor tyrosine-based inhibitory motifs (ITIMs) and a Grb-2 binding motif (Figure 3) (2). X-ray and NMR studies showed that Ig-like domains form Greek-key β-sandwich structures with the varying types differing in the number of strands in the β-sheets as well as in their sequence patterns. By convention, the strands are labeled a to g in sequence with the two strands present between the c and d strands in V domains being labeled c' and c″. One β-sheet consists of strands a, b, e and possibly d while the other contains strands c, f, g and possibly c' and c″. In addition, the C-terminal ends of strands a and g may form a small stretch of parallel β-sheet, disrupting the original strands and giving rise to strands a' and/or g' (3). Ig-like domains are classified into V-type having all strands, C-type (for the C1-set) lacking the c' and c″ strands, S-type (for the C2-set) having the c' strand but not the c″ or d strands and the H-type, which lacks the c″ strand. Ig-like domains usually contain a structural motif composed of cysteine residues generally located in the b and f strands that form a disulfide bridge, and a tryptophan residue located in the c strand (4).
The Shenandoah mutation results in an isoleucine to phenylalanine substitution at position 38 (I38F) in the Siglec-G protein; amino acid 38 is within the V-set Ig-like domain.
Siglec-G is highly expressed on the cell surface all B cell types, with highest expression on B1 cells and conventional B2 cells (2). Siglec-G is also expressed on dendritic cells. In humans, Siglec-10 is expressed on all B cells as well as on eosinophils, monocytes, and a subpopulation of natural killer cells (5).
Siglec-G/-10 is one of two Siglecs expressed by B cells (the other being CD22; see the record for well), and was originally identified as a B cell-associated adhesion protein that functions in the regulation of B cell activation [Figure 4; reviewed by (6)]. Siglec-G/-10 is a B1 cell inhibitory receptor that inhibits B cell receptor-associated NF-κB and calcium signaling, subsequently controlling the expansion and survival of B1 cells (1;2;7;8). The mechanism by which Siglec-G/-10 functions as an inhibitory receptor is unknown. The ITIMs of Siglec-G/-10 are phosphorylated by Src family kinases, creating binding sites for several SH2 domain-containing signaling molecules (e.g., SHP1 [see the record for spin] and SHP2). SHP1 typically promotes the dephosphorylation of intracellular substrates (e.g., PLCγ [see the record for queen], Btk, or SLP65/BLNK [see the record for busy]) and inhibition of several signaling pathways; however phosphorylation of downstream signaling proteins was not changed in B1 or B2 cells from Siglecg-deficient (Siglecg-/-) mice (2). Siglecg-/- B1 cells showed increased expression of the transcription factor NFATc1. The increased calcium signaling in the Siglecg-/- B1 cells putatively causes the increased NFATc1 expression.
Siglec-G inhibits dendritic cell cross-presentation by impairing MHC class I-peptide complex formation (9). Siglecg-/- mice generated more antigen-specific cytotoxic T lymphocytes (9). CD8α+ dendritic cells from the Siglecg-/- mice exhibited more MHC class I-peptide complexes than wild-type CD8α+ dendritic cells (9). The increased number of complexes was due to SHP1-mediated dephosphorylation of the NADPH oxidase component p47(phox) and inhibition of NOX2 activation on phagosomes. Subsequently, exogenous antigens showed excessive hydrolysis and reduced MHC class I-peptide complex formation.
Siglec-G on host antigen-presenting cells negatively regulates graft-versus-host disease (GVHD) through an interaction with CD24 on donor T cells (10).
Siglec-G is essential during RNA virus infection. Siglec-G induces the recruitment of SHP2 and the E3 ubiquitin ligase c-Cbl to the RNA virus sensor RIG-I (11). SHP2 and c-Cbl subsequently promote RIG-I degradation. Inactivation of Siglec-G protects mice against RNA virus infection due to increased type I interferon production.
Siglecg-/- mice have increased levels of serum IgM and produce more IgM autoantibodies than wild-type mice (2;7). Over time, the Siglecg-/- mice develop B-cell lymphoproliferative disorders, including diffuse large B-cell lymphoma, follicular lymphoma, medium-to-large B-cell monomorphic lymphoma and atypical lymphoproliferations (12). Older Siglecg-/- mice also exhibited an autoimmune phenotype with increased autoantibody levels and mild glomerulonephritis as well as increased numbers of plasma cells, germinal center B cells, and activated CD4 T cells (13;14).
The phenotype of the Shenandoah mice indicate loss of Siglec-GShenandoah function.
1) 94°C 2:00
The following sequence of 475 nucleotides is amplified (chromosome 7, + strand):
1 gatgtcactg ctgctgttcc tgctgtcctt cctgttggat ggtgagtggg tccaaggcca
Primer binding sites are underlined and the sequencing primers are highlighted; the mutated nucleotide is shown in red.
1. Hutzler, S., Ozgor, L., Naito-Matsui, Y., Klasener, K., Winkler, T. H., Reth, M., and Nitschke, L. (2014) The Ligand-Binding Domain of Siglec-G is Crucial for its Selective Inhibitory Function on B1 Cells. J Immunol. 192, 5406-5414.
2. Hoffmann, A., Kerr, S., Jellusova, J., Zhang, J., Weisel, F., Wellmann, U., Winkler, T. H., Kneitz, B., Crocker, P. R., and Nitschke, L. (2007) Siglec-G is a B1 Cell-Inhibitory Receptor that Controls Expansion and Calcium Signaling of the B1 Cell Population. Nat Immunol. 8, 695-704.
3. Bork, P., Holm, L., and Sander, C. (1994) The Immunoglobulin Fold. Structural Classification, Sequence Patterns and Common Core. J Mol Biol. 242, 309-320.
4. Smith, D. K., and Xue, H. (1997) Sequence Profiles of Immunoglobulin and Immunoglobulin-Like Domains. J Mol Biol. 274, 530-545.
5. Munday, J., Kerr, S., Ni, J., Cornish, A. L., Zhang, J. Q., Nicoll, G., Floyd, H., Mattei, M. G., Moore, P., Liu, D., and Crocker, P. R. (2001) Identification, Characterization and Leucocyte Expression of Siglec-10, a Novel Human Sialic Acid-Binding Receptor. Biochem J. 355, 489-497.
6. Nitschke, L. (2009) CD22 and Siglec-G: B-Cell Inhibitory Receptors with Distinct Functions. Immunol Rev. 230, 128-143.
7. Ding, C., Liu, Y., Wang, Y., Park, B. K., Wang, C. Y., Zheng, P., and Liu, Y. (2007) Siglecg Limits the Size of B1a B Cell Lineage by Down-Regulating NFkappaB Activation. PLoS One. 2, e997.
8. Jellusova, J., Duber, S., Guckel, E., Binder, C. J., Weiss, S., Voll, R., and Nitschke, L. (2010) Siglec-G Regulates B1 Cell Survival and Selection. J Immunol. 185, 3277-3284.
9. Ding, Y., Guo, Z., Liu, Y., Li, X., Zhang, Q., Xu, X., Gu, Y., Zhang, Y., Zhao, D., and Cao, X. (2016) The Lectin Siglec-G Inhibits Dendritic Cell Cross-Presentation by Impairing MHC Class I-Peptide Complex Formation. Nat Immunol. 17, 1167-1175.
10. Toubai, T., Hou, G., Mathewson, N., Liu, C., Wang, Y., Oravecz-Wilson, K., Cummings, E., Rossi, C., Evers, R., Sun, Y., Wu, J., Choi, S. W., Fang, D., Zheng, P., Liu, Y., and Reddy, P. (2014) Siglec-G-CD24 Axis Controls the Severity of Graft-Versus-Host Disease in Mice. Blood. 123, 3512-3523.
11. Chen, W., Han, C., Xie, B., Hu, X., Yu, Q., Shi, L., Wang, Q., Li, D., Wang, J., Zheng, P., Liu, Y., and Cao, X. (2013) Induction of Siglec-G by RNA Viruses Inhibits the Innate Immune Response by Promoting RIG-I Degradation. Cell. 152, 467-478.
12. Simonetti, G., Bertilaccio, M. T., Rodriguez, T. V., Apollonio, B., Dagklis, A., Rocchi, M., Innocenzi, A., Casola, S., Winkler, T. H., Nitschke, L., Ponzoni, M., Caligaris-Cappio, F., and Ghia, P. (2014) SIGLEC-G Deficiency Increases Susceptibility to Develop B-Cell Lymphoproliferative Disorders. Haematologica. 99, 1356-1364.
13. Muller, J., Lunz, B., Schwab, I., Acs, A., Nimmerjahn, F., Daniel, C., and Nitschke, L. (2015) Siglec-G Deficiency Leads to Autoimmunity in Aging C57BL/6 Mice. J Immunol. 195, 51-60.
|Science Writers||Anne Murray|
|Illustrators||Diantha La Vine|
|Authors||Jin Huk Choi, Xue Zhong, Evan Nair-Gill, Bruce Beutler|